Brightness control device for light emitting display of electronic meter

• US 4,358,713 A
• Filed: 09/25/1980
• Issued: 11/09/1982
• Est. Priority Date: 09/25/1979
• Status: Expired due to Term

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Senoo, Tetsuo, Kogawa, Kouichi
• Primary Examiner(s): La Roche, Eugene R.
• Application Number:
  US06/190,831
• Time in Patent Office: 775 Days
• Field of Search: 315/77, 315/169.1, 315/202, 315/209 R, 315/291, 315/307, 315/178, 315/201, 315/210, 315/250, 315/294, 315/295, 315/312, 340/767
• US Class Current: 315/291
• CPC Class Codes: B60Q 3/16 Circuits; Control arrangements
• CPC Class Codes: H05B 39/047 with pulse width modulation from a DC power source
• CPC Class Codes: H05B 41/3927 by pulse width modulation H05B41/3922 takes precedence

Abstract

A brightness control device for a light emitting display of an automotive vehicle electronic meter wherein the brightness of the light emitting display is controlled in response to the variable duty factor output pulse signal produced by an illumination controller for an illumination lamp of an ordinary meter. A circuit is provided for securing the minimum brightness of the light emitting display. The circuit is rendered operative when a lighting switch is turned off to limit the amplitude of a pulse voltage applied to one terminal of the light emitting display.

Claims

1. A brightness control device for a light emitting display of an electronic meter for use with an illumination controller which generates a pulse signal having a variable duty factor and which is connectable to an illumination lamp when a lighting switch is turned on,

said brightness control device comprising:

(a) a brightness control circuit for generating a control pulse volage to be applied to the light emitting display in response to the pulse signal to control the brightness of the light emitting display in response to the duty factor of the pulse signal; and

(b) a minimum brightness securing circuit for reducing the amplitude of said control pulse voltage when the lighting switch is turned off to secure a minimum brightness of the light emitting display.

2. A brightness control device as claimed in claim 1, further comprising a switch means for disconnecting the illumination lamp from the illumination controller when the lighting switch is turned off.

3. A brightness control device as claimed in claim 2, wherein said switch means comprises a relay having a relay coil connected to the lighting switch and a pair of relay contacts connected between an output terminal of the illumination controller and the ground side terminal of the illumination lamp.

4. A brightness control device as claimed in claim 1, wherein said brightness control circuit is connected to the illumination controller to always receive the pulse signal.

5. A brightness control device as claimed in claim 1, wherein said brightness control circuit applies said control pulse voltage to the light emitting display at a cathode terminal thereof.

6. A brightness control device as claimed in claim 5, wherein said brightness control circuit comprises a transistor connected between a cathode terminal of the light emitting display and ground, the base of said transistor being controlled in response to said pulse signal.

7. A brightness control deivce as claimed in claim 5, wherein said minimum brightness securing circuit limits the maximum voltage of said control pulse voltage applied to the cathode terminal of the light emitting display.

8. A brightness control device as claimed in claim 7, wherein said minimum brightness securing circuit comprises:

a series circuit of a zener diode and a switching transistor connected to the cathode terminal of the light emitting display and the ground, and wherein said switching transistor is switched to its conductive state when the lighting switch is turned off.

9. A brightness control device as claimed in claim 1, further comprising a nighttime brightness lowering circuit for limiting the minimum voltage of said control pulse voltage applied to the cathode terminal of said light emitting display for dimming said light emitting display when the lighting switch is turned on.

10. A brightness control device as claimed in claim 9, wherein said nighttime brightness lowering circuit comprises:

a zener diode connected between an output terminal of said brightness control circuit and the cathode terminal of the light emitting display; and

a switching transistor connected in parallel with said zener diode, and wherein said switching transistor is switched to its conductive state when the lighting switch is turned off.

11. A brightness control device for a light emitting display of an electronic meter of an automotive vehicle, said device comprising:

(a) a lighting switch;

(b) means for generating a pulse signal having a variable duty factor;

(c) means for generating a pulse voltage to be applied to a cathode terminal of the emitting display in response to said pulse signal, said pulse voltage generating means comprising;

a transistor connected between a cathode terminal of the light emitting display and ground, a base of said transistor being controlled in response to said pulse signal;

(d) means for securing a minimum brightness of said light emitting display, said minimum brightness securing means comprising;

a series circuit of a zener diode and a switching transistor connected to the cathode terminal of said light emitting display and the ground, and wherein said switching transistor is switched to its conductive state when the lighting switch is turned off; and

(e) means for dimming said light emitting display, said dimming means comprising;

a zener diode connected between an output terminal of said pulse voltage generating means and the cathode terminal of the light emitting display; and

a switching transistor connected in parallel with said zener diode of said dimming means, said switching transistor of said dimming means being switched to its conductive state when the lighting switched is turned off.

12. A brightness control device for a light emitting display of an electronic meter of an automotive vehicle, said device comprising:

(a) a lighting switch;

(b) an illumination controller for generating a pulse signal having a variable duty factor to control the intensity of an illumination lamp connected to a current source through said lighting switch, wherein an output terminal of said illumination controller is connected to a ground terminal of the illumination lamp;

(c) means for disconnecting the illumination lamp from said illumination controller when said lighting switch is turned off, said disconnecting means comprising;

a relay having a relay coil connected to a current source through said lighting switch and relay contacts connected between the output terminal of said illumination controller and a ground terminal of said illumination lamp;

(d) a brightness control circuit for generating a pulse voltage in response to said pulse signal to be applied to a cathode terminal of the light emitting display of the electronic meter, said brightness control circuit comprising;

a transistor connected between a cathode terminal of the light emitting display and the ground, the base of said transistor being controlled in response to said pulse signal;

(e) a minimum brightness securing circuit for securing a minimuim brightness of the light emitting display comprising;

a series circuit of a zener diode and a transistor connected between the cathode terminal of the light emitting display and the ground, said switching transistor being switched to its conductive state when the lighting switch is turned off; and

(f) a nighttime dimming circuit for limiting the minimum voltage of said pulse voltage applied to the cathode terminal of the light emitting display for dimming said light emitting display, said nighttime dimming circuit comprising;

a zener diode connected between an output terminal of said brightness control circuit and the cathode terminal of the light emitting display; and

a switching transistor connected in parallel with said zener diode, said switching transistor of said nighttime dimming circuit being switched to its conductive state when the lighting switch is turned off.

13. A brightness control device for a light emitting display of an electronic meter of an automotive vehicle, comprising:

(a) a lighting switch;

(b) an illumination controller for generating a pulse signal having a variable duty factor for controlling the intensity of the illumination lamp connected to a current source through said lighting switch, said illumination controller comprising a first output terminal connected to a ground terminal of the illumination lamp and a second output terminal for controlling the brightness of the light emitting display of the electronic meter;

(c) a brightness control circuit responsive to said pulse signal for generating a pulse voltage to be applied to a cathode terminal of the light emitting display of said electronic meter, said brightness control circuit comprising;

a transistor connected between a cathode terminal of the light emitting display and ground, the base of said transistor being controlled in response to said pulse signal;

(d) a minimum brightness securing circuit for securing the minimum brightness of the light emitting display comprising;

a series circuit of a zener diode and a switching transistor connected to the cathode terminal of said light emitting display and ground, said switching transistor being switched to its conductive state when the lighting switch is turned off; and

(e) nighttime dimming circuit for limiting the minimum voltage of said pulse voltage applied to the cathode terminal of said light emitting display for dimming said light emitting display, said nighttime dimming circuit comprising;

a zener diode connected between the output terminal of said brightness control circuit and the cathode terminal of the light emitting display; and

a switching transistor connected in parallel with said zener diode, said switching transistor of said nighttime dimming circuit being switched to its conductive state when the lighting switch is turned off.

14. A brightness control device for a light emitting display of an electronic meter for use with an illumination controller which generates a pulse signal having a variable duty factor and which is connectable to an illumination lamp of an ordinary meter when a lighting switch is turned on,

said brightness control device comprising:

(a) a brightness control circuit for generating a pulse voltage to be applied to the light emitting display in response to the pulse signal to control the brightness the light emitting display in response to the duty factor of the pulse signal; and

(b) a minimum brightness securing circuit comprising a series resistor of a zener diode and a switching transistor connected between the cathode terminal of said light emitting display and ground, said switching transistor being switched to its conductive state when the lighting switch is turned off, wherein said brightness control circuit applies said pulse voltage to the light emitting display at a cathode terminal thereof, and wherein said minimum brightness securing circuit limits the maximum voltage of said pulse voltage applied to the cathode terminal of said light emitting display.

15. A brightness control device for a light emitting display of an electronic meter for use with an illumination controller which generates a pulse signal having a variable duty factor and which is connected to an illumination lamp of an ordinary meter when a lighting switch is turned on,

said brightness control device comprising:

(a) a brightness control circuit for generating a pulse voltage to be applied to the light emitting display in response to the pulse signal to control the brightness of the light emitting display in response to the duty factor of the pulse signal;

(b) a minimum brightness securing circuit which is operative when the lighting switch is turned off to limit the amplitude of said pulse voltage to secure the minimum brightness of the light emitting display; and

(c) a nighttime brightness lowering circuit for limiting the minimum voltage of said pulse voltage applied to the cathode terminal of said light emitting display for dimming said light emitting display when the lighting switch is turned on, wherein said nighttime brightness lowering circuit comprises;

a zener diode connected between an output terminal of said brightness control circuit and the cathode terminal of the light emitting display, and a switching transistor connected in parallel with said zener diode, said switching transistor being switched to its conductive state when the lighting switch is turned off.